Continuation of work initiated during the previous years of this grant will involve studies related to the total syntheses of the macrolide antibiotics methymycin and boromycin. A novel lactonization method, employed successfully in a recent, total synthesis of the macrodiolide vermiculine, will be explored for its scope and generality. The development and use of synthesis methodologies for the stereo-controlled transformation of functional groups in complex molecular structures will play a prominent role in this research.